Molten metal injector system and method

ABSTRACT

The molten metal injector system includes a holder furnace containing a supply of molten metal. A casting mold is supported above the holder furnace. The mold defines a mold cavity for receiving molten metal from the holder furnace. One or more molten metal injectors is supported from the bottom side of the mold. The injector is in fluid communication with the mold cavity and includes a reciprocating piston for pumping molten metal upward from the holder furnace and injecting the molten metal into the mold cavity. The injector is partially submerged in molten metal when the holder furnace contains molten metal. The injector includes a molten metal intake for receiving molten metal into the injector. The molten metal intake is located below the surface of the molten metal in the holder furnace.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of application Ser. No.09/609,997, filed Jul. 3, 2000, entitled “Molten Metal Injector Systemand Method”, which claims the benefit of U.S. Provisional ApplicationSerial Nos. 60/142,218, filed Jul. 2, 1999, entitled “Molten MetalInjector System” and 60/142,315, filed Jul. 2, 1999, entitled “ValvelessMolten Metal Injector System”.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

[0002] The subject matter of this application was made with UnitedStates government support under Contract No. 86X-SU545C awarded by theDepartment of Energy. The United States government has certain rights tothis invention.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to a casting apparatus and to amethod for producing ultra large, thin-walled components and, moreparticularly, to a molten metal injector system for producing ultralarge, thin-walled components.

[0005] 2. Description of the Prior Art

[0006] The manufacturers of ground transportation vehicles, such asautomobiles, sport utility vehicles, light trucks, vans, buses andlarger capacity trucks, have made major efforts in recent years toreduce vehicle weight. Weight reductions reduce harmful atmosphericemissions and increase fuel efficiency of ground transportationvehicles. Presently, a majority of the body components for groundtransportation vehicles are formed from individual steel components thatare assembled via resistance spot welding. For example, the floor panframe of an automobile is normally constructed from a number ofindividual steel stampings that are spot welded together. It would beadvantageous to produce body components for ground transportationvehicles, such as the floor pan frame of an automobile, as a singleultra large casting. As a result, the costs associated with producingmultiple steel stampings and then assembling the stampings may beeliminated. The same technology would also be suitable for components inthe aerospace industry.

[0007] There are several known methods for producing thin-walledcastings. Examples include: high pressure cold chamber vacuum diecasting, premium sand casting, a level pour process practiced by Alcoa,Inc. for producing components for the aerospace industry and lowpressure hot chamber injection. Low pressure hot chamber injection isparticularly well-suited for producing components made from non-ferrousmetals having a low melting point, such as aluminum, brass, bronze,magnesium and zinc.

[0008] A typical casting apparatus and method known in the prior art forthe casting of low melting point temperature metal materials isdisclosed in U.S. Pat. No. 4,991,641 to Kidd et al. (hereinafter “theKidd patent”). The Kidd patent discloses an apparatus that includes asupply tank configured to contain molten metal alloys and a cylinder inthe tank having at its base a connection to an injection passageway thatleads through the tank to a casting die located outside the tank. Apiston reciprocates in the tank, which allows the molten metal alloy tobe drawn into the cylinder and forced through the injection passagewayto the casting die. A control system for the piston controls the speedof the piston in the cylinder when the molten metal alloy is fed to thecasting die. Other similar prior art casting devices are disclosed inU.S. Pat. No. 5,082,045 to Lambert; U.S. Pat. No. 5,181,551 to Kidd etal.; and U.S. Pat. No. 5,657,812 to Walter et al. Each of the devicesdisclosed in the foregoing patents includes a reciprocating piston thatinjects molten metal into a mold cavity during the downstroke of thepiston.

[0009] Piston arrangements such as those disclosed by the Kidd patenthave several disadvantages. For example, the use of reciprocatingpistons that inject molten metal to a casting die during the downstrokehave a tendency to disturb the metal oxide film surface of the moltenmetal alloy contained in the supply tank. Consequently, undesirablemetal oxides and/or air bubbles are often injected into the casting moldalong with the molten metal alloy, thus resulting in an inferiorcasting. Even if the metal oxide film surface of the molten metal alloyis not substantially disturbed, metal oxides sometimes form in thepiston cylinder during the downstroke of the piston.

[0010] Accordingly, it is an object of the present invention to providean apparatus and method for the casting of inexpensive, thin-walledcomponents. In addition, it is an object of the present invention toprovide an apparatus and method for casting thin-walled components ofsuch size and complexity that traditional stamping assemblies made frommultiple stamped components could be replaced with a single, thin-walledcomponent. Finally, it is an object of the present invention togenerally overcome the deficiencies of the prior art such as thosedescribed herein in connection with the Kidd patent.

SUMMARY OF THE INVENTION

[0011] The above objects are accomplished with a molten metal injectorsystem according to the present invention. The molten metal injectorsystem of the present invention includes a holder furnace for containinga supply of molten metal having a metal oxide film surface. A castingmold is supported above the holder furnace and has a bottom side facingthe holder furnace. The mold defines a mold cavity for receiving themolten metal from the holder furnace. A molten metal injector issupported from the bottom side of the mold and projects into the holderfurnace. The injector is in fluid communication with the mold cavity andincludes a piston positioned within a piston cavity defined by acylinder for pumping the molten metal upward from the holder furnace andinjecting the molten metal into the mold cavity under pressure. Thepiston and cylinder are at least partially submerged in the molten metalwhen the holder furnace contains molten metal. The cylinder furtherincludes a molten metal intake for receiving the molten metal into thepiston cavity. The molten metal intake is located below the metal oxidefilm surface of the molten metal when the holder furnace contains themolten metal.

[0012] The molten metal intake is preferably located sufficiently belowthe metal oxide film surface when the holder furnace contains moltenmetal such that the metal oxide film surface remains substantiallyundisturbed during pumping of the molten metal from the holder furnaceto the mold cavity. The piston may be oriented substantiallyperpendicular to the bottom side of the mold and movable through adownstroke and a return stroke. The injector may further include alifting mechanism positioned above the metal oxide film surface when theholder furnace contains the molten metal. The lifting mechanism ispreferably operatively connected to the piston for moving the pistonthrough the downstroke and the return stroke. The molten metalpreferably flows through the molten metal intake and into the pistoncavity during the downstroke of the piston when the holder furnacecontains the molten metal. During the return stroke of the piston, themolten metal received in the piston cavity is preferably pumped upwardfrom the holder furnace by the piston and injected into the mold cavityunder pressure.

[0013] The molten metal intake may be a valve configured to open duringthe downstroke of the piston and permit inflow of the molten metal intothe piston cavity such that metal oxides are substantially preventedfrom forming in the piston cavity. In addition, the molten metal intakemay be a gap formed between the piston and a tapered inner surface ofthe cylinder at a substantially full downstroke position of the piston.Furthermore, the molten metal intake may be an aperture formed in asidewall of the cylinder and connected to the piston cavity. Theaperture may be open for inflow of the molten metal into the pistoncavity when the piston is in the substantially full downstroke position.A molten metal filter may be used to cover the molten metal intake forfiltering and removing debris from the molten metal flowing into thepiston cavity through the molten metal intake.

[0014] The piston and the cylinder are preferably made of a materialcompatible with molten aluminum alloys. The lifting mechanism may be arack and pinion. The piston cavity may be in fluid communication withthe mold cavity through a fill tube passing through the bottom side ofthe mold. A source of inert gas may be in fluid communication with thefill tube such that during the downstroke of the piston, the pistoncavity is filled with inert gas flowing down the fill tube forsubstantially preventing the formation of metal oxides in the cylinder.

[0015] The present invention is also a method of operating a moltenmetal injector in connection with a supply of molten metal and a castingmold having a mold cavity. The method preferably includes the steps of:providing the supply of molten metal; providing the molten metalinjector, with the injector having a cylinder defining a piston cavityhousing a reciprocating piston, with the cylinder including a moltenmetal intake for receiving molten metal from the supply of molten metalinto the piston cavity, and with the piston movable through a downstrokeand a return stroke by a lifting mechanism operatively connected to thepiston; supporting the injector above the supply of molten metal suchthat the cylinder and piston are at least partially submerged in thesupply of molten metal, and such that the molten metal intake liescompletely submerged in the supply of molten metal; moving the pistonthrough a downstroke with the lifting mechanism; permitting inflow ofthe molten metal from the supply of molten metal into the piston cavitythrough the molten metal intake during the downstroke of the piston suchthat the piston cavity is at least partially filled with the moltenmetal; moving the piston cavity through a return stroke with the liftingmechanism; and preventing the inflow of the molten metal from the supplyof molten metal into the piston cavity with the molten metal intakeduring the return stroke of the piston.

[0016] The method according to the present invention may also includethe steps of: locating casting mold above the supply of molten metalsuch that a bottom side of the casting mold faces the supply of moltenmetal; supporting the injector from the bottom side of the casting mold;and placing the piston cavity in fluid communication with the moldcavity such that during the return stroke of the piston the molten metalreceived in the piston cavity through the molten metal intake isinjected into the piston cavity.

[0017] Further, the method according to the present invention mayinclude the steps of: providing the molten metal intake as a valvehaving a valve controller operatively connected thereto for opening andclosing the valve; opening the valve with the valve controller duringthe downstroke of the piston such that the valve permits the inflow ofthe molten metal from the supply of molten metal into the piston cavity;closing the valve with the valve controller during the return stroke ofthe piston such that the valve prevents the inflow of the molten fromthe supply of molten metal into the piston cavity. The method mayfurther include the steps of: supplying inert gas to the piston cavityduring the downstroke of the piston for preventing the formation ofmetal oxides in the piston cavity; and filtering the molten metalflowing into the piston cavity through the molten metal intake duringthe downstroke of the piston with a molten metal filter.

[0018] Further details and advantages of the present invention willbecome apparent from the following detailed description, in conjunctionwith the drawings, wherein like parts are designated with primedreference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a partial cross-sectional side view of a molten metalinjector system according to the present invention;

[0020]FIG. 2 is a front cross-sectional view of an injector for themolten metal injector system of FIG. 1 according to a first embodimentof the present invention;

[0021]FIG. 3 is a side cross-sectional view of the injector of FIG. 2;

[0022]FIG. 4 is a top plan view of the injector of FIG. 2;

[0023]FIG. 5 is a cross-sectional view of an injector for the moltenmetal injector system of FIG. 1 according to a second embodiment of thepresent invention;

[0024]FIG. 6 is a cross-sectional view of an injector for the moltenmetal injector system of FIG. 1 according to a third embodiment of thepresent invention;

[0025]FIG. 7 is a partial cross-sectional side view of a casting moldand the injector used in the molten metal injector system of FIG. 1;

[0026]FIG. 8 is a side view of the molten metal injector system of FIG.1 having multiple injectors in accordance with the present invention;and

[0027]FIG. 9 is a cross-sectional plan view taken along lines IX-IX inFIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]FIG. 1 shows a molten metal injector system in accordance with thepresent invention and designated with reference numeral 10. The injectorsystem 10 generally includes a holder furnace 12 that contains a supplyof molten metal 14, such as a molten aluminum alloy, a casting mold 16positioned above the holder furnace 12, and at least one injector 18supported from the casting mold 16. The molten metal 14 contained in theholder furnace 12 may be exposed to the atmosphere and a metal oxidefilm surface 20 will form at the top of the molten metal 14 contained inthe holder furnace 12. Alternatively, the holder furnace 12 may furtherinclude a cover (not shown) such that the molten metal 14 is enclosedwithin the holder furnace 12. The holder furnace 12 is in fluidcommunication with a main melter furnace 22, which typically contains alarge quantity of the molten metal 14 while the holder furnace 12contains a much smaller quantity of molten metal 14. For example, themain melter furnace 22 may contain 30,000 pounds of the molten metal 14while the holder furnace 12 may contain about 2,000 pounds of the moltenmetal 14. The main melter furnace 22 maintains a steady supply of themolten metal 14 to the holding furnace 12 during operation of theinjector system 10. When the molten metal 14 is a containment-difficultmolten metal, such as molten aluminum alloys, the holder furnace 12 ispreferably lined with refractory material 24 such as Sigma or BETA IICastable refractory material products manufactured by Permatech.

[0029] The casting mold 16 is supported by a support surface 26, such asthe floor of a structure. The casting mold 16 is configured for castingultra large, thin-walled components such as those that may be used inground transportation vehicles. An ultra large, thin-walled componentpart for a ground transportation vehicle may have dimensions approaching3 meters long, 1.7 meters wide and 0.4 meters in depth, and the castingmold 16 will be configured accordingly. The casting mold 16 ispreferably suitable for use with molten metal alloys having a lowmelting point, such as aluminum alloys. The casting mold 16 includes aholder frame 28 that is supported on the support surface 26. The supportsurface 26 is positioned a sufficient distance above the holder furnace12 so that at least portions of the injector 18 lie above the metaloxide film surface 20 of the molten metal 14 contained in the holderfurnace 12. For example, the support surface 26 and, hence, the castingmold 16 may be eighteen inches above the metal oxide film surface 20 ofthe molten metal 14 when the holder furnace 12 is filled with the moltenmetal 14. The casting mold 16 includes a lower die 30 and an upper die32 which together define a mold cavity 34. A cover plate 36 ispositioned on top of the upper die 32. A top clamp plate 38 is separatedfrom the cover plate 36 by a spacer block 40. Hoist rings 42 arepreferably attached to the top clamp plate 3 8 for mold removal andinstallation. A bottom side 44 of the casting mold 16 faces the holderfurnace 12.

[0030] In a preferred embodiment of the present invention, a pluralityof the injectors 18 is supported from the bottom side 44 of the castingmold 16 and project downward into the holder furnace 12. However, inFIG. 1 only one injector 18 is shown for clarity and expediency inexplaining the present invention. The use of multiple injectors 18 tocast an ultra large, thin-walled component will be discussed herein withreference to FIGS. 7-9.

[0031] FIGS. 1-4 show the details of the injector 18 according to afirst embodiment of the present invention. The injector 18 includes acylinder 46 for submerging in the molten metal 14 contained in theholder furnace 12. The cylinder 46 defines a piston cavity 48 and a fillconduit 50 in fluid communication with the piston cavity 48. Thecylinder 46 includes a lower end 52 that is submerged in the moltenmetal 14 contained in the holder furnace 12 when the holder furnace 12is filled with the molten metal 14. At the lower end 52 of the cylinder46, the cylinder 46 defines a tapered inner surface 54. In particular,the tapered inner surface 54 is formed at the lower end 52 of thecylinder 46. The cylinder 46 includes a sidewall 56 having an innersurface 57.

[0032] A piston 58 is positioned in and movable within the piston cavity48. The piston 58 has substantially the same diameter as the pistoncavity 48 and, the tapered inner surface 54 has a slightly largerdiameter than the piston 58. In particular, the piston 58 is movable ina reciprocating manner within the piston cavity 48 through a downstrokeand a return stroke. FIG. 2 illustrates the piston 58 at a substantiallyfull downstroke position in solid lines, and illustrates a full returnstroke position of the piston 58 in broken lines. At the substantiallyfull downstroke position of the piston 58, the piston 58 preferablyremains in contact with the inner surface 57 of the cylinder 46 andprevents inflow of molten metal 14 into the piston cavity 48 at thelower end 52 of the cylinder 46. The total distance the piston 58 mayextend downward may be controlled by a PLC controlling the servomotorspowering the lifting mechanism attached to the piston 58, as discussedhereafter. During the return stroke position of the piston 58, thepiston 58 may close off the fill conduit 50 from the piston cavity 48 asillustrated in broken lines in FIG. 2. The cylinder 46 and the piston 58are preferably made of a material compatible with molten aluminumalloys. In particular, suitable materials for the cylinder 46 and thepiston 58 include graphite and high quality ceramic compounds, such asSialon and Si₃N₄. Additionally, other suitable materials compatible withmolten aluminum alloys include blends of ZrO₂ and BN. Further, thepresent invention envisions the use of both graphite and high qualityceramic compounds for the cylinder 46 and the piston 58.

[0033] Preferably, the piston 58 is oriented substantially perpendicularto the bottom side 44 of the casting mold 16. Hence, during thedownstroke of the piston 58, the piston moves in a direction away fromthe bottom side 44 of the casting mold 16, and during the return strokeof the piston 58 it moves upward toward the bottom side 44 of thecasting mold 16. A fill tube 61 is connected to the fill conduit 50 by aconnecting flange 62 and passes through the bottom side 44 of thecasting mold 16. In particular, the fill tube 61 extends through avertical opening in the holder frame 28 and the lower die 30. The filltube 61 places the piston cavity 48 in fluid communication with the moldcavity 34. The fill tube 61 may be made of materials similar to thoseused for the cylinder 46 and the piston 58.

[0034] The piston 58 is movable through the downstroke and the returnstroke by a lifting mechanism 64 that is fixed to the cylinder 46 by theconnecting flange 62, which is also used to connect the fill tube 61 tothe fill conduit 50. The lifting mechanism 64 is preferably a rack andpinion as shown, but may also be a chain drive. With the cylinder 46substantially submerged in the molten metal 14 contained in the holdingfurnace 12, the lifting mechanism 64 is located above the metal oxidefilm surface 20 of the molten metal 14. In particular, the liftingmechanism 64 is preferably located about fourteen inches above the metaloxide film surface 20 of the molten metal 14 contained in the holderfurnace 12 when the holder furnace 12 contains the molten metal 14. Thelifting mechanism 64 and, hence, the injector 18 are fixed to the bottomside 44 of the casting mold 16 by an upper flange 66. The liftingmechanism 64 may be connected to the upper flange 66 by mechanicalfasteners, i.e., bolts. Similarly, the upper flange 66 may be fixed tothe bottom side 44 of the casting mold 16 by mechanical fasteners, i.e.,bolts. Thus, the injector 18 is attached to the lower die 30 of thecasting mold 16 via the flange 66 and structural connections between theflange 66 and the connecting flange 62.

[0035] Due to the close proximity of the lifting mechanism 64 to theholder furnace 12, the lifting mechanism 64 is subjected to hightemperatures and is preferably made of a material capable ofwithstanding temperatures on the order of 600-1000° F. Suitablematerials for the lifting mechanism 64 include those previouslydiscussed that are compatible with molten aluminum alloys, as well assteel and other ferrous materials since the lifting mechanism 64 doesnot directly contact the molten metal 14. The rack and pinion comprisingthe lifting mechanism 64 may be driven by a remotely controlledservomotor (not shown). The servomotor may be controlled by a PLC. ThePLC may be programmed to adjust the vertical distance the piston 58 maytravel during its downstroke.

[0036] A valve 68 is connected to the cylinder 46 for receiving themolten metal 14 into the injector 18. Hence, the valve 68 operates asthe molten metal intake to the injector 18. The valve 68 is preferablyconnected to the cylinder 46 such that with the cylinder 46 at leastpartially submerged in the molten metal 14 contained in the holdingfurnace 12, the valve 68 is completely submerged in the molten metal 14and located below the metal oxide film surface 20 of the molten metal14. In particular, in a preferred embodiment of the injector 18 thevalve 68 is located about fourteen inches below the metal oxide filmsurface 20 of the molten metal 14, when the holder furnace 12 is filledwith the molten metal 14. The valve 68 is in fluid communication withthe piston cavity 48 and is configured to open at the beginning of thedownstroke of the piston 58 and close during the return or pumpingstroke of the piston 58. The valve 68 preferably opens fully when thepiston 58 begins its downstroke and closes fully when the piston 58reaches its substantially full downstroke piston. The valve 68 remainsclosed during the return or pumping stroke of the piston 58, therebysealing off the piston cavity 48. The opening and the closing of thevalve 68 is controlled by a valve controller 69. The valve controller 69may be a rack and pinion operatively connected to the valve 68. The rackand pinion forming the valve controller 69 may be driven by a remotelycontrolled servomotor. A molten metal filter 70 may be used to cover theinlet to the valve 68 to filter and remove debris from the molten metal14 flowing into the piston cavity 48 through the valve 68. In additionto molten metal filtration, the molten metal filter 70 may regulate theflow of molten metal 14 into the piston cavity 48 so that there is noinitiation of turbulent molten metal flow into the piston cavity 48. Thelifting mechanism 64 controlling the piston 58 may be set to allow thepiston 58 to form a gap with the tapered inner surface 54 of thecylinder 46, which permits the molten metal contained in the pistoncavity 48 to drain from the piston cavity 48 when it is time to performroutine maintenance on the injector 18, or replace the injector 18.

[0037]FIG. 5 shows a second embodiment of the injector according to thepresent invention and designated with reference numeral 18′. Theinjector 18′ shown in FIG. 5 is substantially identical to the injector18 shown in FIGS. 1-4, but now the valve 68 is omitted from the injector18′. The molten metal intake to the piston cavity 48′ is now defmedentirely by a gap 71 formed between the piston 58′ and the tapered innersurface 54′ of the cylinder 46′ when the piston 58′ is extended to thesubstantially full downstroke position. The size of the gap 71 may beadjusted by adjusting the lifting mechanism 64′, which controls thevertical distance the piston 58′ may travel with respect to the cylinder46′. Accordingly, in the injector 18′, at the substantially fulldownstroke of the piston 58′, the piston 58′ extends below the end ofthe cylinder 46′ which permits the gap 71 to be formed between thepiston 58′ and the tapered inner surface 54′ of the cylinder 46′. Thepiston land of the piston 58′ may also be shortened to facilitateformation of the gap 71 between the piston 58′ and the tapered innersurface 54′ of the cylinder 46′. In FIG. 5, the piston 58′ is shown at afull downstroke position where the gap 71 is approximately at a maximumand the rate of inflow of molten metal into the piston cavity 48′through the gap 71 would be approximately at a maximum. A molten metalfilter 70′ may be attached to the lower end 52′ of the cylinder 46′. Forexample, the molten metal filter 70′ may be provided as a sleeveextending downward sufficiently from the lower end 52′ of the cylinder46′ such that the piston 58′ may extend downward to its full downstrokeposition. The molten metal filter 70′ is used to filter the molten metal14 and further, may be used to regulate the flow of molten metal intothe piston cavity 48′ so that initiation of turbulent molten metal flowinto the piston cavity 48′ through the gap 71 is minimized.

[0038]FIG. 6 shows a third embodiment of the injector according to thepresent invention and designated with reference numeral 18″. Theinjector 18″ shown in FIG. 6 is substantially identical to thepreviously discussed injectors 18, 18′, but further includes twoapertures 72 formed in the sidewall 56″ of the cylinder 46″. Theapertures 72 are formed adjacent the tapered inner surface 54″ of thecylinder 46″. The injector 18″ in FIG. 6 includes two apertures 72formed in the cylinder 46″, but it will be appreciated by those skilledin the art that at a minimum only one aperture 72 is necessary. Inaddition, the injector 18″ may have more than two apertures 72 inaccordance with the present invention. The piston land of the piston 58″is formed similar to the piston land of the piston 58 for the injector18 of FIG. 2. The apertures 72 are each covered by a molten metal filter70″ for filtering and straining debris from the molten metal 14 as themolten metal 14 flows through the apertures 72 and into the pistoncavity 48″. The molten metal filter 70″ may be further used to regulatethe flow of molten metal 14 into the piston cavity 48″ so thatinitiation of turbulent molten metal flow into the piston cavity 48″through the apertures 72 is minimal. The apertures 72 are located in thesidewall 56″ of the cylinder 46″ such that the apertures 72 are open forinflow of the molten metal into the piston cavity 48″ when the piston58″ is in the substantially full downstroke position. The apertures 72begin to open for inflow of the molten metal 14 into the piston cavity48″ as the piston 58″ approaches the substantially full downstrokeposition. At the substantially full downstroke position of the piston58″, the piston 58″ preferably remains in contact with the inner surface57″ of the cylinder 46″ and prevents inflow of molten metal 14 into thepiston cavity 48″ at the lower end 52″ of the cylinder 46″ when thepiston reaches the substantially full downstroke position. Hence, theapertures 72 are the molten metal intake to the piston cavity 48″. Asthe piston 58″ begins its return stroke, the outer circumferential edgeof the piston 58″ remains substantially engaged with the inner surface57″ of the cylinder 46″. The lifting mechanism 64″ may be adjusted toallow the piston 58″ to extend below the end of the cylinder 46″ suchthat a gap forms which provides an egress point for molten metal whenthe injector 18″ requires maintenance or replacement.

[0039] Referring now to FIGS. 1-4, operation of the injector 18 througha downstroke and return stroke cycle of the piston 58 will now bediscussed. As stated previously, the injector 18 is supported from thebottom side 44 of the casting mold 16. The cylinder 46 and the piston 58are substantially submerged in the molten metal 14 contained in theholding furnace 12. As the piston 58 begins its downstroke, the valve 68opens and permits the molten metal 14 to flow into the piston cavity 48.As the piston 58 moves through its downstroke, the molten metal 14continues to flow into the piston cavity 48 through the valve 68 and themolten metal filter 70, if present. After a predetermined period of timeto allow the piston cavity 48 to fill with the molten metal 14, thevalve 68 closes and the lifting mechanism 64 is engaged to begin movingthe piston 58 upward through its return stroke. The piston 58 may becontrolled such that the piston cavity 48 may be entirely filled withmolten metal 14 flowing through the valve 68 before the piston 58reaches its substantially full downstroke position and before a gapforms between the piston 58 and the cylinder 46. The vertical distancetraveled by the piston 58 is controlled by the lifting mechanism 64. Theservomotors driving the lifting mechanism 64 and the valve controller 69may be remotely controlled by a programmable logic computer (PLC) tocontrol the distance the piston 58 travels and the opening and closingof the valve 68, as will be appreciated by those skilled in the art.

[0040] For example, a casting cycle may begin with the piston 58 at adownstroke position as shown in FIG. 2. At this point, the valve 68 isclosed, the piston cavity 48 is completely filled with molten metal 14and the lift mechanism's servomotor(s) controlled by the PLC begins theinjection stroke (i.e., return stroke). This follows a pre-specifiedposition versus time path. When molten metal 14 fills the mold cavity34, pressure builds and the servomotor(s) can no longer follow a pathversus distance relation and abruptly changes to a torque holdingcondition. After the torque holding condition is established, whichreflects a pressure intensification of about 5 to 45 psi for asufficient time for the molten metal 14 to solidify in the mold cavity34, the valve 68 is opened and the piston 58 is slowly lowered to thestart position (i.e., downstroke position). The piston 58 may be set totravel any vertical distance required and is not limited to travelingbetween the full downstroke and fill return stroke positions dependingon the application at hand, as will be appreciated by those skilled inthe art. In the case where no valve 68 is present, as shown in FIG. 5,the piston 58′ is lowered sufficiently for molten metal to enter intothe piston cavity 48′ through the gap 71.

[0041] Referring again to FIGS. 1-4, as the piston 58 moves upwardthrough its return stroke, the molten metal 14 now contained in thepiston cavity 48 is pumped upward by the piston 58 from the holderfurnace 12. The molten metal 14 flows through the fill conduit 50 andinto the fill tube 61. The molten metal 14 in the fill conduit 50 andthe fill tube 61 is injected under low pressure (i.e., less than about15 psi) into the mold cavity 34. As the piston 58 reaches thesubstantially full return stroke position, for example, the liftingmechanism 64 is stopped. The piston 58 may be stopped prior to the fullreturn stroke position if the torque holding condition occurs indicatingthat the mold cavity 34 is filled with the molten metal 14. A sensor(not shown) may be attached to the lifting mechanism 64 and used tosense when the piston 58 has reached the torque holding conditionindicating the mold cavity 34 is filled with the molten metal 14. Thesensor may be connected to the PLC controlling the lifting mechanism 64,for example.

[0042] The injector 18 of the present invention advantageously locatesthe valve 68 well below the metal oxide film surface 20 of the moltenmetal 14. Since the valve 68, i.e., the molten metal intake for theinjector 18, is located well below the metal oxide film surface 20, themetal oxide film surface 20 remains substantially undisturbed as themolten metal 14 from the holder furnace 12 flows into the piston cavity48 through the valve 68. As described previously, the valve 68 should belocated about fourteen inches below the metal oxide film surface 20.This assures that any disturbances to the metal oxide film surface 20are minimized and substantially prevents metal oxides from beingintroduced into the piston cavity 48 from the metal oxide film surface20.

[0043] In addition, because the piston cavity 48 is filled during thedownstroke of the piston 58 via the valve 68 this helps prevent theinitiation of turbulent molten metal flow and thus formation of metaloxides in the piston cavity 48 due to the action of the piston 58. Thedifficulty with many prior art piston arrangements is that the pumpingstroke of the piston 15 during the downstroke, which has a tendency todisturb the metal oxide film surface of the supply of molten metal inwhich the piston operates, as well as create disturbances within thepiston cavity which could cause metal oxides to form in the pistoncavity. In the injector 18, the pumping stroke is the return strokewhich minimizes the chances of forming metal oxides in the piston cavity48, as well as minimizes the disturbances to the metal oxide filmsurface 20 of the molten metal 14 in the holder furnace 12. In addition,in the injector 18 the piston cavity 48 is gradually refilled during thedownstroke of the piston 58 with the molten metal 14 slowly enteringthrough the valve 68. The valve 68 permits the inflow of the moltenmetal 14 into the piston cavity 48 such that a vacuum is not generatedin the piston cavity 48 which could pull atmospheric air into the filltube 61 and the fill conduit 50 and further down into the piston cavity48. This substantially prevents the fonnation of metal oxides within thepiston cavity 48 due to the movement of the piston 58. A valve thatregulates the rate of inflow of the molten metal 14 into the pistoncavity may be used in place of the valve 68.

[0044] The injector 18 of the present invention may further include asource of inert gas 80, such as argon or nitrogen, in fluidcommunication with the fill tube 61. The source of inert gas 80preferably supplies the inert gas through the lower die 30 or the upperdie 32 and into the mold cavity 34. The inert gas 80 will flow down thefill tube 61 and fill conduit 50 and into the piston cavity 48. Thisprevents the introduction of atmospheric air into the fill tube 61, fillconduit 50 and the mold cavity 34 which could potentially form metaloxides in the piston cavity 48.

[0045] The injector 18′ of FIG. 5 operates in a substantially similarmanner to the injector 18 of FIGS. 1-4, with the exception that themolten metal 14 from the holder furnace 12 flows into the piston cavity48′ entirely through the gap 71 formed between the piston 58′ and thetapered inner surface 54′ of the cylinder 46′ at the substantially fulldown position of the piston 58′. Accordingly, the molten metal intake tothe piston cavity 48′, the gap 71, is located well below the metal oxidefilm surface 20 of the molten metal 14 in this embodiment, anddisturbances to the metal oxide film surface 20 of the molten metal 14are minimized.

[0046] The injector 18″ of FIG. 6 operates in a substantially similarmanner to the injector 18 of FIGS. 1-4 and the injector 18′ of FIG. 5,with the exception that with the piston 58″ located in the substantiallyfull downstroke position, the apertures 72 in the sidewall 56″ of thecylinder 46″ are open for inflow of the molten metal 14 into the pistoncavity 48″. The filters 70″ covering the apertures 72 act to filter andstrain debris from the molten metal 14 before passing through theapertures 72. As the piston 58″ begins its return stroke, the apertures72 begin to become closed-off by the piston 58″. In this embodiment,because the apertures 72 are located well below the metal oxide film 20,disturbances to the metal oxide film surface 20 are minimized.

[0047] As stated previously, the present invention envisions the use ofa plurality of injectors 18 (or 18′ or 18″) suspended from the bottomside 44 of the casting mold 16, as show in FIG. 8. Referring now toFIGS. 7-9, the injectors 18 are preferably supported from the bottomside 44 of the mold 16 to optimize the inflow of the molten metal 14into the mold cavity 34. FIG. 9 illustrates a possible configuration forarranging the injectors 18 to form a component piece for a groundtransportation vehicle, such as a single piece lift gate for a minivan.In the arrangement of FIG. 9, seven injectors 18 are utilized, with thelocations of the injectors 18 selected to optimize inflow of the moltenmetal 14 into the mold cavity 34 such that the molten metal 14 evenlyfills the mold cavity 34 without the introduction of occlusions that maybe formed by trapped air. The injectors 18 may be individuallycontrolled by a programmable logic controller, for example, such thatthe injectors 18 inject the molten metal 14 at different rates and atdifferent times as necessary to fill the mold cavity 34 to form thecomponent.

[0048] In view of the foregoing, a method of injecting the molten metalinto the mold cavity of the casting mold in accordance with the presentinvention may include the steps of: providing the supply of the moltenmetal; supporting the casting mold above the molten metal, with thebottom side of the mold facing the molten metal; supporting the moltenmetal injectors from the bottom side of the mold, with the injectorsprojecting into the holder furnace and providing fluid communicationbetween the holder furnace and the mold cavity; and injecting the moltenmetal into the mold cavity with the injector such that the metal oxidefilm surface of the molten metal in the holder furnace remainssubstantially undisturbed. The method may further include the step ofindividually controlling the injectors to regulate the injection of themolten metal into the mold cavity of the mold. The injectors areoperated such that metal oxides are substantially prevented from formingwithin the piston cavity for each of the injectors. The step ofinjecting the molten metal from the supply of molten metal into the moldcavity preferably occurs while the piston for each of the injectors ismoving in the return stroke. The method according to the presentinvention may further include the step of supplying inert gas from thesource of inert gas to the piston cavity for each of the injectors, whenthe piston for each of the injectors is moving in the downstroke.Furthermore, the method of the present invention may include the step ofallowing inflow of the molten metal to the cylinder with the valve foreach of the injectors, when the piston for each of the injectors ismoving in the downstroke.

[0049] The injector system of the present invention provides asimplified apparatus and method for casting inexpensive, but highquality thin-walled components. The injector system of the presentinvention may be applied to cast complex components as a single piece,which could be used to replace stamping assemblies made from multiplestamped components. In addition, the injector system of the presentinvention generally overcomes the previously discussed deficiencies withthe prior art. For example, the injector system includes a piston whichpumps molten metal during its return stroke and receives molten metalduring its downstroke. In addition, the molten metal intake in theinjector system is located well below the metal oxide film surface ofthe molten metal. Consequently, during filling of the piston cavity themetal oxide film surface of the molten metal remains substantiallyundisturbed.

[0050] While the preferred embodiments of the present invention weredescribed herein, various modifications and alterations of the presentinvention may be made without departing from the spirit and scope of thepresent invention. The scope of the present invention is defined in theappended claims and equivalents thereto.

We claim:
 1. A method of operating a molten metal injector in connectionwith a supply of molten metal and a casting mold having a mold cavity,comprising the steps of: providing a casting mold defining a moldcavity; supporting at least one molten metal injector from the bottomside of the casting mold, with the injector including a cylinderdefining a piston cavity and a reciprocating piston located within thecylinder, with the cylinder including a molten metal intake forreceiving molten metal into the piston cavity, and with the pistonmovable through a downstroke and a return stroke by a lifting mechanismoperatively connected to the piston; locating a supply of molten metalbelow the casting mold such that the cylinder and piston are at leastpartially submerged in the supply of molten metal and such that themolten metal intake lies submerged in the supply of molten metal, withthe injector providing fluid communication between the supply of moltenmetal and mold cavity; moving the piston through a downstroke with thelifting mechanism; opening the molten metal intake during the downstrokeof the piston to permit inflow of molten metal into the piston cavityfrom the supply of molten metal to at least partially fill the pistoncavity with molten metal; moving the piston through a return stroke withthe lifting mechanism; closing the molten metal intake to preventfurther inflow of molten metal into the piston cavity from the supply ofmolten metal; and injecting molten metal directly into the mold cavitywith the injector.
 2. The method of claim 1, wherein the molten metalintake is a valve, with the valve operable between open and closedpositions by a valve controller, and wherein the method furthercomprises the steps of: opening the valve with the valve controllerduring the downstroke of the piston to permit inflow of molten metalinto the piston cavity from the supply of molten metal; and closing thevalve with the valve controller during the return stroke of the pistonto prevent further inflow of molten metal into the piston cavity fromthe supply of molten metal.
 3. The method of claim 1, further comprisingthe step of supplying inert gas to the piston cavity during thedownstroke of the piston.
 4. The method of claim 1, further comprisingthe step of filtering the molten metal flowing into the piston cavitythrough the molten metal intake with a molten metal filter.
 5. Themethod of claim 1, further including the steps of: providing andsupporting a plurality of molten metal injectors from the bottom side ofthe casting mold, with each of the injectors providing fluidcommunication between the supply of molten metal and mold cavity; andindividually controlling the injectors to regulate the injection ofmolten metal into the mold cavity of the casting mold.
 6. An injectorfor injecting molten metal into a mold cavity of a casting mold,comprising: a cylinder for at least partially submerging in a supply ofmolten metal, with the cylinder defining a piston cavity, and with thecylinder defining a fill conduit in fluid communication with the pistoncavity and extending through a top wall of the cylinder; a pistonpositioned within the piston cavity and movable through a downstroke anda return stroke, wherein the fill conduit extends along an axissubstantially parallel to the piston over its entire length; a liftingmechanism fixed to the cylinder and operatively connected to the pistonfor moving the piston through the downstroke and the return stroke; anda valve connected to the cylinder for receiving molten metal into thepiston cavity when the cylinder and piston are at least partiallysubmerged in the supply of molten metal, wherein the valve is configuredto open during the downstroke of the piston permitting inflow of moltenmetal into the piston cavity when the cylinder and piston are at leastpartially submerged in the supply of molten metal, and wherein the valveis configured to close during the return stroke of the piston preventingthe inflow of molten metal into the piston cavity, and the piston isconfigured to pump the molten metal received in the piston cavity intothe fill conduit for injection into the mold cavity when the cylinderand piston are at least partially submerged in the supply of moltenmetal.
 7. The injector of claim 6, further including a molten metalfilter covering the inlet to the valve for filtering the molten metalflowing into the piston cavity through the valve during the downstrokeof the piston.
 8. The injector of claim 6, wherein the piston and thecylinder are made of materials compatible with molten aluminum andaluminum alloys.
 9. The injector of claim 6, wherein the liftingmechanism is a rack and pinion.